Blood Metals and Cognitive Function in Chinese Workers

Abstract

Background/Aim: The relationship of co-exposure to manganese, aluminum, and copper on neurotoxicity is still unclear. Therefore, our aim was to determine the association of these metals with learning and memory. Methods: We completed a cross-sectional study of 60 Chinese male workers from a ferroalloy or manufacturing factory. Whole blood samples were analyzed for metals using inductively coupled plasma-mass spectrometry. Animal naming, fruit naming, and WHO/UCLA-Auditory Verbal Learning Tests (AVLT) assessed learning and memory. Additional information was obtained via questionnaire. Linear regression models were constructed for each metal with each test, adjusting for age, education, smoking, and alcohol use; a final model included all three metals. Blood lead was assessed, but was not associated with any cognitive tests. Results: Geometric mean blood manganese was 14.0 µg/L (95% confidence interval (CI): 13.0, 15.0), aluminum was 306.1 µg/L (286.2, 327.5), and mean copper was 78.6 µg/dL (76.4, 80.7). Ferroalloy factory workers had significantly higher blood aluminum and manganese, but not higher copper, compared to manufacturing workers. In adjusted models, manganese was significantly associated with poorer AVLT first 5 trial average (β=-1.93; 95% CI: -3.82, -0.03), but was not significant after adjustment for other metals (β=-1.27; -3.10, 0.55). There was a similar pattern for aluminum with AVLT. Aluminum was significantly associated with improved performance on the fruit naming test in adjusted models including manganese, and copper. In models adjusting for covariates, manganese and aluminum, an increase in copper was associated with significantly poorer performance on animal naming (β=-0.238; -0.377, -0.099) and AVLT (β=-0.070; -0.128, -0.013). There was a non-significant association for copper with fruit naming (β=-0.102; -0.207, 0.003). Conclusions: Blood copper was consistently associated with decreased performance on cognitive function testing even after adjustment for manganese and aluminum; this should be verified with studies using metal biomarkers reflecting cumulative exposure.